Friday, July 25, 2014

Japanese Beetles and Roses--2014 Season

Well, it's late July and the Japanese Beetles (JBs) are just about at their peak here in Minneapolis. I would say we're seeing more than last year but not nearly as many as in 2012.  So does that mean it's getting better or worse?  In 2012, a golf course greens keeper told me that most golf courses in our area were using large amounts of imidicloprid (Merit) to protect fairways and greens from the JB grubs.  I attributed the downturn in last year's JB crop to be the result of that practice, since I have two golf courses within a mile of me, which is well within the JB flying range.  My best guess is that the golf courses probably used less imidicloprid in 2013 because of growing awareness that it is the most widely used of the neo-nicotinoid family of insecticides, which have been strongly implicated in bee colony collapse disorder and have been banned in Europe (imidicloprid is made by Bayer in Germany).  Also, I would assume there was less incentive to put it down on the golf courses, with such a sharp reduction in JBs during 2013.  Anyway, they're back again in force, so it's a good time to look again at the best ways to control them.

Here is a key passage from my 2012 article "The Beetles Are Coming, The Beetles Are Coming", as revised in January 2013:

.... Let’s take a look at how to try to control adult JBs on your roses.  Note I said “try” because there is really no completely satisfactory solution.  So, here’s the “secret” of this article: The best way to control JBs is with your fingers and soapy water!  Don’t be fooled by the easy solutions presented by insecticides; just like killing the grubs in your lawn, the JB adults you kill with insecticides are just the tip of the iceberg that is flowing up and down your street into your garden.  The only sure-fire way to deal with JBs is to pick or shake them off your roses into a can of soapy water.  JBs are really quite vulnerable to this method because their primary defense mechanism is to simply drop off the plant they are destroying, down to the dirt or grass.  They don’t sting or bite and they move pretty slowly, especially early in the morning and at dusk, so the “trick” here is to hold your can under the target JBs and pick or shake them off the plant into the soap-water.  I’m as squeamish as the next guy or gal about picking bugs with my fingers, so I wear nitrile surgical or milking gloves (that I get in the dairy-farm department at Fleet Farm) and I use a plastic 2 lb. coffee can (Maxwell House), which has a built-in handle and a big opening.  I squirt a little dishwashing soap in the can and fill it about half full with water.  The soap breaks the surface tension of the water and they are very helpless once they hit it.  While this process is laborious, especially because it goes on for many days, through thousands of JBs, there is some pleasure in watching the little demons meet their end, knowing that every JB I drown will never fertilize or lay an egg for next year’s hatch.  Each night, I dispose of the dead JBs either by flushing them down a toilet or putting them in my yard-waste bin (covered).  Note that they become very smelly if you leave them in the soap-water overnight.

This is important!  Don’t be tempted to squish JBs and throw them on the ground after you pick them off your roses (even though it would give you (and me) so much pleasure to do so).  When you squish a female JB her sexual-attractant pheromone is spewed out and brings in every male in the neighborhood!

Likewise, don’t buy JB traps.  They use that same sexual pheromone to bring JBs to the traps, and many more JBs come into your yard than ever find their way into the traps.  If you are just compelled to buy traps, buy them for your neighbors and keep them out of your own yard!  Oh, and be sure to empty your neighbors’ traps every day, because all those dead JB females just keep attracting more suitors, which are bound to find  your roses.  

The main point here is that insecticides are really not the best answer for controlling JBs.  There is a very effective pyrethroid, that I mention in the article, but it also kills insects like lady bugs (they're beetles too) and other beneficials that eat aphids and thrips.  When you kill them off, you start a vicious cycle of insect infestation, which is far more difficult to control and a lot more work than a few weeks of drowning JBs!

I just issued a blog: "Controlling Spider Mites and Thrips on Roses Without Insecticides" .
So, if I were to spray a pyrethroid on my roses to deter the JBs now, I would negate all the work I describe in this article to introduce predatory mites and attract beneficial insects to my gardens.  I have not seen a single aphid in my gardens this summer because of the beneficials.  Last year, when I aggressively sprayed the pyrethroid for the JBs, I ended up with a major infestation of aphids.  Obviously, I had taken out all their enemies, so then I had to spray another insecticide to stop the aphids.  That's a vicious cycle, and all because I didn't want to drown JBs, i.e. lazy gardening.  What impresses me, however, is how well the beneficials have come back this summer, now that I'm not killing them off.  I really don't want to do that to them again.

As I meander through my rose beds, in the morning and evening (the best times), picking the beetles off the leaves and flowers and popping them in the soapy water, I carry a scissor and a bucket with me for disposing of the deadheads and damaged leaves that I cut off the roses, at the same time. In other words, I find that passing through the gardens several times a day causes me to do a better job of caring for my roses.  That side-effect of the JBs has become an important  part of my gardening routine.

So could JBs actually have a positive effect on a rose garden?  Well, that's a stretch!

Let me know if I can help.


  1. Great article Jack! We are not seeing very many in our area this year! Glad for the break from them. Happy gardening!

    1. Thanks Teresa... I was hoping that our cold winter would freeze out the grubs. No such luck.